User interaction with computers continues to increase each day. More jobs require individuals to interact with computers and more people are choosing to interact with computers for both work and entertainment. Various tracking devices for interacting with a computer include electronic mice, keyboards, joysticks, and touch pads. Other tracking devices, including personal digital assistants (PDAs), cellular telephones, and electronic pens, allow users to interact with different computers and computer systems.
Coupled with the increase in user interaction, there has been an increasing need for more precise interaction. For example, a user can process an image that she captured with her digital camera on a host computer that is running an application program for manipulation of images. She may want to change the color or contrast on certain portions of image to brighten up the green color of the grass or blue color of the sky. In doing so, the user may identify portions of the image to process by using one of the various tracking devices for interacting with the host computer. The user may have an electronic mouse with an actuatable button, allowing the user to press and hold the button to encircle the portion she wishes to process. In such a scenario, the user may wish to have very precise identification of the portions in which to process.
Tracking devices fall into one of two types of systems: a relative tracking system and an absolute tracking system. A relative tracking system has the ability to discern relative motion from one position to another, independent of knowledge of absolute position. Methods of relative optical tracking include image correlation, differential pattern gradient based, laser speckle based and Doppler-based among others. One feature of a relative tracking system is that one or more sensors detect signals that change over time and can be processed in various ways to determine changes in relative position. An absolute tracking system has the ability to discern a position of the device irrespective of a previous determination. Computer input devices such as electronic mice and trackballs implement relative tracking systems while electronic pens commonly implement absolute tracking systems. Tracking devices typically do not include both relative and absolute tracking systems. Cost, size, and difficulty in combing the two from a technological standpoint have left manufactures choosing from one of the two methods when constructing their respective devices. As such, when a user operates an input device for interacting with one computer, she may not be able to interact properly with another computer or more precisely with the one computer. A user must have two different devices for performing the different methods of tracking.